The pure rotational spectrum of CoO(X4Δi): Identifying the high-spin components

New measurements of the pure rotational spectrum of the CoO radical in its X4Δi state (v = 0 and v = 1) have been conducted using millimeter-wave direct absorption techniques. CoO was created by the reaction of cobalt vapor and N2O. Spectra arising from the Ω = 3/2 and 1/2 spin levels, both which exhibit Λ-doubling, have been recorded, as well as from the Ω = 7/2 and 5/2 ladders, which have been studied in the past. Rotational, fine structure, Λ-doubling and hyperfine parameters for the v = 0 and v = 1 states have been established from a global analysis of all four spin components. The data suggest a near-by 4Σ state.